You can get 3 compressed blues out using that idea you just need to do two things:
1. Set the stack size override to 8 on all 12 inserter placing on belts.
2. SLOW the inserters placing on the entrance to the UG belts by 1 tick

That is a simple 48(47? forget offhand) tick clock with the insteres wired up to be enabled on 'A' = 1. This slows them just enough that the gap between sets of items are just big enough for the opposite stack inserter to fill in the gap.